Desalting a forced flow steam generator



April 7, 1964 G. PETER DESALTING A FORCED FLOW STEAM GENERATOR Filed001:. 17, 1960 .7 n ven f 0 r: 60 TTFR/ED PETER PA rcwr Anogyay m fir MWMP 7 a g Q f MP 0 4 cox N no N a m: 9 m. J 87 33 77 7 u 4 w Tu Ar 4 7 8\w g W W w. aw L m, a m H W 3 m 35w 2 a f? WWW 1 7/. 6 7 Pd Bl 7 7 H 3 r8 M H M 3 4m ,7 w 5 mm A a 5i 6 m 0 M All. A 5:: 1' L 7 United StatesPatent 0 F 3,127,747 DESALTTNG A FURCED FLOW STEAM GENERATOR GottfriedPeter, Wlnterthnr, Swizerland, assignor to Sulzer Freres, S.A.,Winterthur, Switzerland, a corporation of Switzerland Filed @et. 17,15960, Ser. No. 63,133 Claims priority, application Switzerland Oct. 3%,1959 1 Claim. (Cl. 60-67) The present invention relates to a method andapparatus for desalting a forced flow steam generator, more particularlya forced flow steam generator operating at the critical orsupercr-itical pressure of water whereby portions of pipe lines formingthe tubular heat transfer system of the steam generator and subject tosalt deposits are periodically washed out by the operating medium of thesteam generator. if the steam generator is operated at critical orsupercrit-ical pressure, the pressure in the pipe line which is washedout is reduced to subcritical pressure in order to produce Wet steamwhose liquid phase dissolves the salt deposits.

In conventional forced flow steam generators operating at subcriticalpressure salt depositions in the tube system of the generator areimpeded and the water circulating through the steam power plan-t ofwhich the steam generator forms a part is simultaneously desalted byproviding a liquid separator at the outlet of the portion of the tubesystem of the steam generator wherein the water is converted into thesteam, the liquid phase of the operating medium being blown down fromthe separator. Since the major part of the salts present in theoperating me dium is in the liquid phase, the salts are removed from thecircuit together with the blowdown liquid.

This desalting method is not suitable for a steam generator operating atthe critical or at supercritical pressure, because in these generatorsthere is no definite difference between the liquid and the steam phaseof the operating medium and the transition from the liquid phase to thesteam phase is not sudden but continuous. Salts contained in thefeedwater of a forced flow steam generator operated at critical orsupercritical pressure are usually deposited in the zone of the highpressure tube system where the operating medium reaches criticalconditions and where there is a relatively great increase of the specific volume of the operating medium. The salts separated in thistransition zone from the liquid to the steam phase and deposited on theinside of the heating tubes must be periodically removed by washing out.done according to present operating practice by providing a check valveat the outlet of each of the tube lines which are arranged in parallelrelation with respect to the flow of the operating medium and form thetubular heating sys tem of the steam generator, and by connecting avalve pipe to each of the aforesaid tube lines in the neighborhood andupstream of the respective check valve. When a valve in one of the pipesis opened the pressure in the respective tube line is reduced to asubcritical pressure and the check valve at the outlet of the tube lineto which the pipe is connected closes. The result is that wet steamflows through the tube line whereby salts deposited therein aredissolved and carried out of the steam generator by the wet steam andremoved from the circuit of the steam power plant of which the steamgenerator forms a part.

The 'amount of operating medium needed for washing out the individualtube lines of the tubular heating sys tem of a forced flow steamgenerator may be quite great and it is important that the heat andenergy loss caused by removing the washing fluid from the system is heldas small as possible by recovering at least a portion of the heat andpressure energy contained in the operating me- Tnis 1S 7 3,127,747Patented Apr. 7, 1964 dium which has been used for washing out. Thewashingout operation should not disturb the operation of the steamgenerator and the turbines receiving operating steam therefrom, i.e.,the temperature and amount of live steam leaving the steam generatorshould not be affected by the washingcut operation.

Lt is an object of the invention to provide a system for Washing out theheating tubes of a forced flow steam generator which tubes are arrangedin parallel relation with respect to the flow of the operating fluidtherethrough, without substantially affecting the quality of theproduced steam and the continuity of steam production.

A further object of the invention is to provide a system for recoveringat least a portion of the thermal energy contained in the part of theoperating medium which has been used for washing out a tube line formingpart of the tubular heating system of a forced flow steam generator, bytransferring heat from the washing fluid to the feedwater of the steamgenerator. In a modification of the system the washing fluid isseparated into a liquid phase and into a steam phase, the latter beingintroduced into the steam part of the cycle of the power plant of whichthe steam generator forms a part or used for indirectly heating afeedwater preheater. The liquid phase is preferably used for indirectlypreheating feedwater.

A further object of the present invention resides in the provision ofapparatus for recovering at least a portion of the thermal energycontained in the part of the operating medium which has been used forwashing out a tube line forming part of the tubular heating system of aforced flow steam generator, particularly of a steam generator operatingat critical or supercritical pressure whereby the washing fluid isconducted through heat exchangers interposed in the flow of theoperating fluid through the power plant of which the steam generatorforms a part, for transferring heat from the washing fluid to theoperating fluid and/ or washing fluid is returned to the operating fluidin the part of the cycle of the steam power plant outside of the steamgenerator for utilizing the heat and pressure energy contained in thewashing fluid. In a modification of the system according to theinvention the washing fluid which has been used for Washing out a tubeline of the steam generator is passed through a separator wherein theliquid phase of the washing fluid is separated from the steam phase; thesoobtained liquid phase is conducted through one or more heat exchangersfor transferring heat to the feedwater of the steam generator and thesteam phase is conducted to a turbine forming part of the steam powerplant which includes the steam generator, for converting thermal energycontained in the steam phase to mechanical power. Alternatively, thesteam phase may be used for heating feedwater which is under highpressure and the liquid phase may be used for transferring heat tofeedwater which is under low pressure.

In plants wherein the Washing-out operation is not continuous so thatthere are periods of time when no washingout fluid is available forfeedwater heating, the missing heat may be derived from steam tappedfrom a turbine forming part of the power plant which includes the steamgenerator. In this case it is preferred to effect the switch fromWashing-out fluid as a heating medium to tapped steam as a heatingmedium by automatically actuating valves in response to the pressure inthe pipe line which normally conducts the washing fluid to the heatexchanger or heat exchangers.

The novel features which are considered characteristic of the inventionare set forth with particularity in the appended claims. The inventionitself, however, and additional objects and advantages thereof will bestbe understood from the following description of an embodiment thereofwhen read in connection with the accompanying drawing, the single figureof which is a diagrammatic Layout of a steam power plant according tothe invention.

Referring more particularly to the drawing, numeral 1 designates acondenser from which condensate is pumped by a low pressure feed pump 2through low pressure preheaters 3 and 3a to a container 4. A highpressure teed pump 5 draws water from the container 4 and pumps itthrough high pressure preheaters 6 and 6a to a forced flow steamgenerator 7. The steam generated therein is superheated in a superheater8 wherefrom the steam is conducted to a first turbine 9 and partlyexpanded. The steam leaving the turbine 9 enters a second turbine it)the exhaust of which is conducted into the condenser 1.

The steam generator 7 includes a heating tube system consisting of .aplurality of tube lines connected in parallel relation with respect tothe flow of the operating medium, four tube lines 11 being shown. Theinvention, however, is not restricted to steam generators having thisnumber of parallel tube lines. At the end of each tube line 11 a one-wayor check valve 12 is provided which permits flow of operating medium inone direction only, namely out of the tube lines 11. The outlets of thevalves 12 are connected to a collector 13 from which the operatingmedium is conducted through a pipe 14 into heating tubes 15. Water isconverted into steam in the tubes 11, Le. upstream of the valves 12, andit is in these tubes where salt contained in the feedwater may bedeposited. The tubes 15 contain only steam when the plant is in normaloperation and no salt is deposited therein. Close to and upstream of thevalves 12 a pipe provided with a valve 16 is connected to each of thetubes 11. These pipes are connected to a pipe 17 through. which thefluid leaving the individual tubes 11 through the valves 16 is conductedto the high pressure feedwater preheater 6a which is of the indirectheat exchanger type. The operating medium received in the heater 6a fromthe pipe 17 leaves the heater 6a through a pipe 18 and is conducted tothe low pressure 'feedwater preheater 3a wherefrom the operating mediumis conducted either through a pipe line 39 as heating agent to thefeedwater heater 3 or is blown down through a pipe 37. The pipe line 18is connected to the container 4 by a pipe 23 in which a valve 33 isinserted which will be described later.

The valves 16 are periodically opened, one after another, so that thereis either no or only one valve 16 open at a time. Opening of one of thevalves 16 causes a pressure drop in the respective tube line 11 belowthe critical pressure so that the operating fluid passes as wet steamthrough the open valve 16 into the pipe 17 Presence of wet steam in thetube line 11 causes solution of salts which have previously beendeposited in the tube line. The wet steam or washing fluid also carriesalong such impurities as are not soluble at the prevailing pressures andtemperatures of the fluid in the tube line The wet steam which has actedas a washing fluid in the tube line 11, which is connected by the openvalve 36 to the pipe line 17, consecutively transfers heat in thepreheaters 6a and 3a to the feedwater. A part of the washing fluid isreintroduced through pipe 23 into the feedwater in the container 4.

By transferring heat from the operating fluid which has been used aswashing fluid, in the preheaters 6a and 3a to the feedW-ater land bydirect return of a portion of the washing fluid to the teedwater, aconsiderable portion of the heat energy is recovered which wouldotherwise be lost.

The high pressure feedwater preheater 6a is selectively connected to thepipe line 17 or to a pipe 31 which is connected to the turbine 9 andincludes a valve 30. A valve 32 is provided in the pipe line 18. Thevalves 30, 32 and 33 are operated in response to the pressure prevailingin the pipe 31 which pressure acts on a pressure sensitive device 34causing opening of the valves 30, 32. and 'closing'of the valve 33 whenthe pressure in the pipe 31 drops below a predetermined value. If thepressure in the pipe 31 rises above the predetermined value, the valves30 and 32 are closedand the valve 33 is opened. The second turbine 10 isconnected to the low pressure feedwater heater 3a by a bleeder conduit35 in which a valve 36 is interposed. Blowdown water is removed from thepreheater 3a through the pipe 37 provided with a valve 38. The pipe 39is connected to the pipe 37 upstream of the valve 38. The pipe 39 isprovided with a valve 40 and conducts blowdown water from the preheater3a through the feedwater preheater 3 which is upstream of the preheater3a, into the condensate flowing from the condenser 1 to the feed pump 2.The valves 36, 38 and 49 are controlled in response to the pressureprevailing in the bleeder conduit 35 downstream of the valve 36 by meansof a pressure sensitive device 41 which causes opening of the valves 36and 4t) and closing of the valve 33 upon dropping of the pressure in theconduit 35 below a predetermined value, and vice versa.

The illustrated arrangement is preferably used in plants where cyclicoperation of the valves 16 is not possible so that there are periods oftime when no washing fluid is available as heating agent for thefeedwater preheaters. As long as washing fluid is available due toopening of one of the valves 16 the high pressure preheater 6a and thelow pressure preheater 3a receive Washing fluid through the pipes 17 and18 upon opening of the valves 32 and 38. If the washing operation isstopped, all valves 16 are closed and the pressure in the pipes 17 and31 drops. This causes the pressure responsive device 34 to open thevalves 30 and 33 and to close the valve 32. Partly expanded steam tappedfrom the first turbine 9 now flows through the valve 36 and the pi es 31and 17 to the high pressure preheater 6a and from the latter through thepipes 18 and 23 and through the valve 33 into the container 4. Closingof the valve 32 causes dropping of the pressure in the pipe 18downstream of the valve 32 and in the conduit 35. Under these conditionsthe pressure responsive device 41 opens the valves 35 and 40 and closesthe valve 38. The low pressure preheater 3a which under these conditionsdoes not receive any Washing fluid is now heated by steam tapped fromthe tubine 10. This steam flows through the conduit 35 and the pipe 39back into the circuit of the operating fluid in the steam power plantupstream of the low pressure feed pump 2.

Although the present invention is particularly suited for steamgenerators operating at critical or supercritical pressure and describedin this combination, the invention may also be advantageously used incombination with forced flow steam generators operating at subcriticalpressures, particularly if it is desired to omit a water separatorinterposed in the main stream of the operating medium.

I claim:

In a stream power plant in which operating fluid moves in a circuitincluding a forced flow steam generator operating at least at thecritical pressure of water, a prime mover connected for steam flow tosaid steam generator for converting thermal energy of the steam tomechanical power, means connected to said prime mover for receivingsteam therefrom and condensing the steam, and means connected to saidcondensing means for receiving condensate therefrom and returning thecondensate as feedwater to said steam generator, said last mentionedmeans including feedwater preheating means, said steam generatorincluding a heating tube system comprising a plurality of tube linesarranged in parallel relation with respect to the flow of operatingfluid therethrough, a check valve placed at the outlet of each of saidtube lines permitting flow of operating fluid out of said tube lines andpreventing backing up of operating medium into said tube lines, a valvedpipe connected to each of said tube lines upstream of the respectivecheck valve for relieving operating medium from the individual tubelines by I. opening the respective valved pipe for Washing out therespective tube line, a Washing fluid conduit connected to all of saidvalved pipes for receiving the Washing fluid relieved by said valvedpipes, said washing fluid conduit 6 responsive means connected to saidpipe downstream of said valve and to said valve for opening said valveupon a pressure drop in said pipe below a predetermined pressure and forclosing said valve upon an increase of the being connected to at leastone of said feedwater pre- 5 pressure in said pipe above saidpredetermined pressure.

heating means for conducting Washing fiuid thereto and transferring atleast a part of the thermal energy contained in the Washing fluid to theoperating fluid moving in the circuit, a pipe interconnecting saidwashing fluid conduit and said prime mover for tapping steam from thelatter, a valve interposed in said pipe, and pressure References Citedin the file of this patent UNITED STATES PATENTS 1,942,861 Huster Jan.9, 1934 10 2,842,103 Profos July 8, 1958 2,900,792 Buri Aug. 25, 1959

